This invention relates to a novel laminating film which is effective in extending the life of photographic prints, especially those displaying color images. Although the specific embodiments described hereinafter relate to the protection of photographic prints, the invention may also be used to extend the life of graphics, documents, and other like objects which are subject to gradual deterioration, particularly due to fading.
The fading of photographic prints, especially color photographs made with chromogenic dyes, is a slow but continuously progressive process principally caused by ultraviolet radiation, cycling relative humidity, high temperature, atmospheric pollution and oxidation. Because the fading process progresses slowly over a period of years, the eye tends to adjust to such gradual changes, and the fading is not usually noticed until substantial deterioration has occurred and the condition has become irreversible.
By the use of the present invention, the fading process is greatly deterred over a period of time long enough to enable photographic color prints to be used for archival purposes.
There have been several attempted solutions to the problem of photographic print deterioration, but the common shortcoming of the prior art is that the protective materials specified are likely to themselves deteriorate within a period of time substantially shorter than that required for archival life.
U.S. Pat. No. 2,578,282 of Bliss, issued Dec. 11, 1951, discloses a laminate for application of a photographic element which is not subject to spectral reflection of light from the laminate. The laminate comprises the following layers: gelatin, gelatin and cellulose nitrate, cellulose acetate, and a surface layer of cellulose acetate and pigment. Such a laminate can be expected to give short-term protection against humidity and abrasion. However, the materials specified are not known to filter out ultraviolet radiation and are themselves susceptible to degradation in a period substantially shorter than that required for archival life.
U.S. Pat. No. 3,397,980 of Stone, issued Aug. 20, 1968, discloses a protective laminate for photographic film having micro-images formed thereon. The laminate comprises a durable outer layer, such as polyethylene terephthalate (Du Pont's Type D MYLAR) and an inner layer of polyethylene. The laminate is bonded to the photographic film by a polyvinyl acetate binder which bonds to both the emulsion coating of the photographic film and the polyethylene. Unless the polyethylene terephthalate contains an ultraviolet absorber, not contemplated by this patent, the photograh will not be protected from excessive ultraviolet radiation exposure. Moreover, the polyethylene layer of the laminate, as well as the polyvinyl acetate binder, are both subject to relatively rapid photodegradation. Thus, while the laminate disclosed in this patent can provide protection of the photographic film against humidity and abrasion, it will not impart archival qualities to a photograph that is exposed to normal room lighting over a period of years.
U.S. Pat. No. 4,077,830 to Fulwiler, issued Mar. 7, 1978, discloses another type of laminate used as a protective sheet over the emulsion surface of a photograph. The laminate is characterized by a pressure sensitive adhesive with a very smooth surface to avoid optical distortions. The laminate comprises a protective sheet not more than 0.001 inch thick, preferably formed of Du Pont's MYLAR polymer, and a coating of an adhesive, preferably an acrylic adhesive less than 0.001 inch thick. The patent specifically states that the adhesive transmits, rather than filters out, a major portion of ultraviolet light. Since ultraviolet light is a major cause of photographic fading, the laminate of this patent cannot be expected to inhibit fading, although it can be expected to provide a certain amount of protection against humidity and abrasion.
In addition to laminates of the type disclosed in the foregoing patents, there are various types of coatings in liquid form that have been applied to photographs and the like to provide varying degrees of protection. However, such coatings are difficult to apply uniformly, particularly without a precision coating machine, and liquid coatings do not provide as effective a barrier to humidity and atmospheric pollution as does a solid polymeric film. Examples of such coatings are disclosed in U.S. Pat. No. 2,632,701 of Salminen et al., issued Mar. 24, 1953, U.S. Pat. No. 3,028,252 to Mones et al., issued Apr. 3, 1962, U.S. Pat. No. 3,079,837 to Theilemann, issued Mar. 5, 1963, U.S. Pat. No. 3,190,197 of Pinder, issued June 22, 1965, U.S. Pat. No. 3,460,961 of Young et al., issued Aug. 12, 1969, U.S. Pat. No. 3,473,929 of Jeffreys et al., issued Oct. 21, 1969, U.S. Pat. No. 3,931,431 of Giorgi, issued Jan. 6, 1976, U.S. Pat. No. 4,049,861 of Nozari, issued Sept. 20, 1977, and U.S. Pat. No. 4,156,046 of Lien et al, issued May 22, 1979.
U.S. Pat. No. 3,506,470 of Young et al., issued Apr. 14, 1970, discloses photoprints coated with compositions which have an outer surface that rearranges under the influence of ultraviolet light to protect the photoprints from the effects of the ultraviolet light. The composition is disclosed as being applied in the form of solutions or in the form of free films cast from the solutions. The compositions disclosed in this patent are quite different from the materials used in the laminate of the present invention.
The present invention overcomes the principal problems associated with the prior art protective laminates and coatings. The laminates of the present invention provide an effective barrier against all of the known causes of photographic deterioration except temperature and, most significantly, are designed to provide that protection for substantially longer periods of time than the prior art.